Characteristics of activated chars prepared by fluidized bed pyrolysis for SO2 adsorption and NO reduction with ammonia

Abstract

Activated chars were prepared by fluidized bed pyrolysis at temperature rangd between 500$^\circ$C and 800$^\circ$C from coals of three different ranks and studied for their sulfur capture capacity and catalytic activities in the selective catalytic reduction (SCR) of nitric oxide with ammonia. The capacity for adsorbing sulfur dioxide and catalytic activities were examined with the thernogravimetric analyzer (Cahn 2000) and a fixed bed integral reactor, respectively. In the preliminary test, we selected and characterized the chars and commercially available active carbons in order to determine the appropriate design parameters for a moving bed unit. Subsequently, the performance tests of the moving bed system using lignite char as a candidate catalyst were carried out. A fluidized bed system was used to pyrolyze coals. It consists of a fluidized bed, coal feeder, char discharger, heating element, cyclone, gas supply system, and tar recovery system. The fluidized bed was made of Inconel pipe whose inside diameter and length were 0.1 m and 0.6 m, respectively. The chars used as sample were discharged continuously from the fluidized bed through an overflow line during pyrolysis. All the chars obtained from different pyrolysis condition and commercial active carbons from different sources were submitted to careful elemental (the amount of oxygen is assessed by difference) and proximate analyses. Minerals in the ash were also determined by Atomic Absorption Spectrometer (AAS), Inductived Coupled Plasma Atomic Emission Spectrometer (ICP-AES), and Oxygen Bomb Sulfur Analyzer. Visual examinations of surface texture, shape, and pore of the chars were made with a Hitachi S-2500C scanning electron microscope using a 30 kv beam. Surface area measurement of the char catalyst was carried out with carbon dioxide adsorption at 298 K in conventional apparatus. The amount of surface oxygen functional groups was meaured with temperature programmed desorption (TPD). TPD experimen...